The TTB ‘s Alcohol Beverage Sampling Program is TTB’s survey of products in the marketplace. In short, the TTB purchases product from retailers and tests them to be sure the products inside the bottles match the claims displayed on the labels.
The results of the sampling program over the past few years, according to TTB, “show that proofing and gauging of distilled spirits is a problem area for some industry members.” The TTB adds, “because the excise tax for distilled spirits is based on alcohol content, proper gauging of distilled spirits is a vital factor in proper tax determination.”
To be sure you are in compliance, review the gauging manual found in 27 CFR part 30 and the official methods used by TTB Scientific Services Division.
Here is a link to the 2013 survey: